Angiotensin II is a multifunctional peptide hormone which regulates blood pressure and fluid balance as well as acting as a growth factor for some cell types. Angiotensin II acts on a variety of target tissues through cell surface guanine nucleotide regulatory protein (G-protein) coupled receptors, and while multiple receptor subtypes have been identified, most known functions are mediated through the AT1A receptor subtype. AT1A expression and signaling pathways through which receptor couple occur in a tissue specific manner. The cellular control of these processes in not known. Recently, the messenger RNA 3' untranslated region of many genes has been identified as an important regulator of the mRNA transcript itself, as well as the translated product. In this application, we present evidence that the 3' untranslated region of the AT1A has a significant role in dictating the coupling of this receptor to intracellular signaling pathways. In particular, the coupling of the AT1A to [specific G-protein,] cAMP modulation and growth responses (hyperplasia/hypertrophy) are determined by the 3' untranslated region. The mechanisms by which the 3' untranslated region of the AT1A receptor can dramatically alter the function of its translated protein is the primary focus of this proposal. We have additional evidence to support the hypothesis that specific mRNA binding proteins recognize sequences within the 3' untranslated region of the AT1A mRNA and, thereby, alter cell function. We propose to characterize the 3' untranslated region of the AT1A mRNA to understand the biochemistry and tissue specific expression and signaling of this important receptor. Specifically, we will first determine the regulatory role of AT1A 3' untranslated region in controlling receptor function and identify the functional changes and alterations in signaling events. Second, we will determine the sequences in the 3' untranslated region which control receptor function by interacting with mRNA binding proteins and elucidate the mechanisms employed by the 3' untranslated region in controlling physiological responses. Third, we will identify and clone the cDNAs of the mRNA binding proteins inorder to determine the functional significance of mRNA binding proteins interacting with specific 3' untranslated region sequences of the receptor. Understanding the mRNA binding proteins and their role in the regulation of biological functions of specific proteins like the AT1A will provide insight into the coordinate actions responsible for regulating cellular functions and coupling to signaling pathways. In a broader sense, clarification of AT1A function at the molecular level will contribute to our understanding of the renin angiotensin system (primarily Angiotensin II actions on AT1A) in controlling normal physiological homeostasis as well as the association of aberrations of the system in disease states.